The present invention relates to a rotating speed detecting device of a rotary type electrostatic spray painting device.
The speed of rotation of a rotary shaft is normally detected by sensing a change in the reluctance of a magnetic circuit which is formed between an electromagnetic pick-up and a nut screwed onto the rotary shaft, or between an electromagnetic pick-up and a spacer fixed onto the rotary shaft. The sensing function is performed by the electromagnetic pick-up. However, it is necessary in such known systems to arrange the electromagnetic pick-up at a position near the nut or the spacer. Consequently, situations where a large space cannot be provided around the rotary shaft, such as in a rotary type electrostatic spray painting device, it is difficult to detect the rotating speed of a rotary shaft by using such an electromagnetic pick-up. In addition, in order to use an electromagnetic pick-up in a rotary type electrostatic spray painting device to which a negative high voltage is applied, it is necessary to enclose the electromagnetic pick-up with an electrical insulating material so that the negative high voltage does not have an adverse effect on the output signal. However, enclosing the electromagnetic pick-up causes its size to become even larger. Consequently, it is difficult to arrange an electromagnetic pick-up at a position near the rotary shaft of a rotary type electrostatic spray painting device, and it is therefore difficult to detect the rotating speed of the rotary shaft by using such a conventional electromagnetic pick-up.
It is, therefore, an object of the present invention is to provide a rotating speed detecting device which is suited for a rotary type electrostatic spray painting device to which a negative high voltage is applied.